1. Field of the Invention
This invention relates to a laser welding device and a method of checking laser welding condition which is provided at the time of welding to monitor plasma caused by concentrically irradiating laser beams to an object so as to determine whether the laser welding condition is good or not.
2. Description of Prior Art
In laser welding technique, a laser output measurement device has been used to control energy level of laser beams generated at the time of the laser welding. FIG. 12 shows a schematic view of an energy level measuring system of laser beams with the laser output measurement device employed.
In FIG. 12, laser beams 6 generated by a laser oscillator 1 are applied on a measurement portion 11 of the laser output device through an optical fiber 2, light-converging lenses 3, 4 and a protective glass 5 so as to display an energy level of the laser beams 6 on a display device 12. An energy level value on the display device 12 makes it possible to recognize an energy intensity of the laser beams 6.
In YAG laser welding device, there is provided a laser energy monitoring member referred to as a laser output monitoring device 25 which has often been used to control an energy level of laser beams. FIG. 13 shows a schematic view of an energy level measuring system of laser beams with the laser output monitoring device 25 employed.
In FIG. 13, a part of laser beams 6 radiated from a laser source 21 of the laser oscillator 1 is passed through a semi-reflective mirror 22 to measure an energy level of the laser beams 6 by a detector 23 so as to display it on a display device 24. The detector 23 has a photodiode and a solar cell so as to recognize an energy intensity of the laser beams 6 radiated from the laser oscillator 1.
However, in the laser welding technique, even when the energy level of the laser beams 6 radiated from the laser oscillator 1 is constant, the energy level of the laser beams 6 is subject to change so as to attenuate the laser energy due to damage and stain on optic-related components such as the optical fiber 2 and the light-converging lenses 3,4 located between the laser oscillator 1 and the object. It also holds true when a distance between the laser oscillator 1 and the object is subject to change so as to vary the laser energy density at the time of replacing the objects or the like.
Since the laser output measurement device is normally used before and after the laser welding operation so as to confirm whether or not the energy level of the laser beams 6 is subjected to change by comparing the energy level before the laser welding operation and the one after the laser welding operation, it is difficult to use the laser output measurement device concurrently during the laser welding operation.
In the laser output monitoring device 25 which serves as an output value measuring device of the laser oscillator 1, the device remains immune to positional changes of the optical fiber and the light-converging lenses 3,4, and the device has no direct relation to measuring the laser energy level of the welding portion on which the laser beams 6 are applied.
In both the laser output measurement device and the laser output monitoring device 25, therefore, it is impossible to detect the welding condition of the object on which the laser beams 6 are applied.
This necessitates to frequently carry out a sampling inspection for breaking test, X-rays photographing and chemical analysis so as to increase the number of manufacturing steps. When the product is inspected as defect during the sampling operation, all the rest of the product lot have to be rejected, thus adding an unnecesary step during the manufacturing working.
Therefore, it is one of the objects of the invention to provide laser welding device and a method of checking a welding condition which is capable of determining whether or not the welding condition is good while concurrently carrying out the welding operation.